Alginate coarse/nanoemulsions containing Zataria multiflora Boiss essential oil as edible coatings and the impact on microbial quality of trout fillet

In this study, the effect of edible coarse/nanoemulsions of alginate as coating containing Zataria multiflora Boiss essential oil (ZEO) on the microbial quality of fish fillets was investigated at three concentrations (i.e. 0.25%, 0.5% and 1% [w/v]) in 16 days of storage at 4°C. Moreover, a comparison was made between the fabricated coarse emulsion and nanoemulsion coatings by particle size and polydispersity index analyses. Sample analysis was performed with regard to total viable count (TVC), total psychrophilic count (TPC), hydrogen sulphide‐producing bacteria count (HSC) and Enterobacteriaceae count (ENC) on days 0, 4, 8, 12 and 16. According to the findings, all the samples showed increased microbial counts during the storage periods. The highest reduction rates of TVC (about 2 log CFU/g), TPC (about 1 log CFU/g), HSC (about 1.5 log CFU/g) and ENC (about 3 log CFU/g) were observed in the nanoemulsion of alginate containing 1% w/v ZEO (NE 1%) samples, compared with alginate and control samples. The microbial growth was significantly inhibited in all treatments, compared with that in the control (p < .05). Accordingly, it can be concluded that nanoemulsion coating was more effective than coarse emulsion to prolong the durability of fish fillets and revealed a faster and greater inhibition of microbial flora, compared with coarse emulsions during the storage time.     

Antimicrobial Activity of 1% Cetylpyridinium Chloride Against Listeria spp. on Fish

Cetylpyridinium chloride (CPC) was evaluated as an antimicrobial against Listeria monocytogenes (LM) and Listeria innocua (LI) on fish. LI and LM showed the same reduction profile and the same minimum inhibitory and bactericidal concentrations. When CPC was applied to a diced fish matrix, reductions of 3.17–3.26 and 3.07–3.19 log were determined for LI and LM, respectively. Antimicrobial activity of CPC against LI resulted in initial reductions of 2.8–3.1 log in fresh fish fillets, 0.9–1.1 log in smoked fish fillets, and 3.2–3.4 log on fish skin. Effectiveness of CPC against total plate counts on fish skin showed reductions of 2.4–2.9 log.     

The Effects of Sodium Alginate on Quality of Rainbow Trout (Oncorhynchus mykiss) Fillets Stored at 4 ± 2°C

Edible coating is a novel food packaging technology for controlling the growth of spoilage bacteria and chemical changes in ready-to-eat food products. Fresh fish are highly perishable foodstuffs and are very susceptible to spoilage. A sodium alginate coating was used to maintain the quality of rainbow trout fillets in chilled storage over a period of 20 days. Fillet samples were coated with an aqueous solution of 3% sodium alginate and then stored at chilled temperature (4 ± 2°C). The control and coated samples were analyzed periodically (every 5 days) for microbial (aerobic plate count and psychrotrophic count), chemical (total volatile basic nitrogen, thiobarbituric acid, peroxide value), and sensory characteristics. The results indicated that the sodium alginate coating helped protect the quality characteristics of treated fresh fish fillets and prolonged the shelf life during chilled storage of rainbow trout fillets.     

Effect of Trisodium Phosphate or Water Dip on the Survival of Salmonella and Listeria monocytogenes Inoculated Catfish Before and After Freezing

Salmonella and Listeria monocytogenes (LM) are occasional contaminants on raw fish. Catfish fillets were artificially contaminated with LM and Salmonella, dipped in a 1.5 % (30 min) trisodium phosphate solution (TSP), and cryogenically frozen. After 3 months frozen storage, Salmonella (2 log), but not LM, was inactivated on the fillets treated with the dip. This indicates that TSP dip followed by cryogenic freezing can be used to control Salmonella, but not LM, on catfish fillets.     

Effects of Sodium Alginate and Chitosan Coating Combined with Three Different Essential Oils on Microbial and Chemical Attributes of Rainbow Trout Fillets

ABSTRACT

Meat products, such as fish meat, are known to be susceptible to undesirable chemical and microbial reactions that characterize spoilage. In this study, the effect of a sodium alginate and chitosan coating incorporated with Mentha piperita, Artemisia dracunculus, and Zataria multiflora essential oils on chemical and microbial attributes of rainbow trout meat was evaluated during storage at 4°C. Chemical and microbial assays were performed on rainbow trout fillets with alginate and chitosan coatings and 0.2% concentration of test essential oils. The results showed that the alginate coating with essential oils significantly decreased production of thiobarbituric acid (TBA) and total volatile basic nitrogen (TVBN) and reduced the growth of foodborne spoilage bacteria during storage at 4ºC. At day 12, the best results were obtained in chitosan coating + Z. multiflora, with 5.96 ± 0.12, 4.93 ± 0.12, and 3.83 ± 0.2 for total viable counts, psychrotrophic bacterial count, and lactic acid bacteria count, respectively. Moreover, the lowest amounts of chemical analysis were observed in chitosan coating + Z. multiflora at the final day (0.54 ± 0.03 and 20.31 ± 0.1 for TBA and TVBN, respectively). Our study revealed that essential oils can be used as effective natural components against undesirable chemical and microbial reactions in fish meat.     

Effects on Lipid Oxidation and Bioactive Properties of Rainbow Trout Fillets Fed with Barley

Barley concentrations ranging from 0% to 32% were incorporated into rainbow trout (Oncorhynchus mykiss) diets. The effect of barley concentration on lipid peroxidation and antioxidant activity of fish fillets were analyzed. Results showed that the inclusion of barley in rainbow trout diets had an inhibitory effect on lipid oxidation, probably associated with certain bioactive compounds in barley that could interact with scavenging and reducing metabolites involved in lipid oxidation. Concentrations up to 8% of barley produced fish fillets with high antioxidant activity and higher levels of alpha-tocopherol.     

Edible Corn‐zein‐based Coating Incorporated with Nisin or Lemongrass Essential Oil Inhibits Listeria monocytogenes on Cultured Hybrid Striped Bass,Morone chrysops × Morone saxatilis,Fillets During Refrigerated and Frozen Storage

Listeria monocytogenes presents a serious threat to consumer safety because it is resistant to various food storage techniques, including reduced or modified atmosphere packaging, refrigerated storage, and increased salt concentration. Edible coatings incorporated with natural antimicrobials have been suggested to control pathogenic and spoilage bacteria on a variety of meat products. In this study, edible zein‐based coatings incorporated with nisin and lemongrass essential oil (LGEO; 8%) were evaluated for antibacterial action against L. monocytogenes and spoilage organisms on fresh, cultured hybrid striped bass, Morone saxatilis × Morone chrysops, under two storage conditions (refrigerated or frozen) and two packaging types (polyvinyl chloride [PVC] and vacuum packing) over time. Corn‐zein‐based edible coatings were found to be an effective carrier for nisin and LGEO. Fillets coated with nisin showed the largest decrease in L. monocytogenes cell counts in both PVC and vacuum‐packaged samples in both refrigerated and frozen product, while fillets coated with LGEO showed intermediate inhibition of L. monocytogenes cell counts, with the strongest LGEO antibacterial effect being found in frozen product regardless of packaging. Both nisin and LGEO treatments were most effective in PVC‐packaged fillets compared to vacuum‐packaged fillets, but the difference in bacterial loads between packaging methods was minor. Bacterial loads on refrigerated product tended to increase slightly after 5‐d storage regardless of coating treatment or packaging, whereas bacterial loads on frozen product remained stable or decreased with time up to 60 d regardless of coating treatment or packaging. Data from the present study indicate that application of edible coatings incorporated with essential oils not only promotes food product safety but also may satisfy the preferences of consumers.     

Chilled Storage of Pangasianodon hypophthalmus Fillets Coated with Plant Oil Incorporated Alginate Gels: Effect of Clove Leaf,Clove Bud,Rosemary and Thyme Oils

Essential oil incorporated alginate coating provides a novel way to improve the safety and shelf life of pangasius (Pangasianodon hypophthalmus) fillet. Oils from the leaves and buds of clove, flowering tops of rosemary, and dried seeds of thyme were incorporated separately in alginate coating. All the plant oils showed antibacterial activity, but the zone of inhibition was relatively larger for thyme oil. Alginate coating was performed using sodium alginate (1.5%), glycerol (10%), and calcium chloride (2%) and plant oil at 1% (v/v). The coated fillets were stored under chilled conditions and samples were analyzed for bacteriological, chemical, sensory, color, and texture parameters. Psychrotrophic counts crossed 7 log cfu/g by the 13^th day and 15^th day of chilled storage in control and plant oil treated fillets, respectively. The peroxide value of treated fillets was relatively low. Texture profile analysis indicated that plant oil incorporated alginate coating reduced the rate of loss of texture (softening) during chilled storage. Plant essential oil incorporated alginate gels were relatively better compared to control fillets in preserving pangasius fillet quality during chilled storage, and incorporation of thyme oil was relatively better compared to clove leaf oil, clove bud oil, and rosemary oils.     

Listeria monocytogenes is inhibited on fillets of cold‐smoked sunshine bass,Morone chrysops × Morone saxatilis,with an edible corn zein‐based coating incorporated with lemongrass essential oil or nisin

Ready‐to‐eat (RTE) foods have been identified as a high‐risk food group because of the number of outbreaks caused by food‐borne pathogens isolated from these products. As these items receive no further processing or heat treatment prior to consumption, bacterial pathogens such as Salmonella, Staphylococcus aureus, Escherichia coli, and Listeria monocytogenes present a serious threat to consumer safety. Of particular concern, L. monocytogenes is resistant to various food storage techniques, including reduced or modified atmosphere packaging, refrigerated storage, and increased salt concentration. Cold‐smoked fishery products have been implicated in a number of listeriosis cases, where it is estimated that between 6 and 36% of cold‐smoked fish is contaminated with L. monocytogenes. Edible coatings incorporated with natural antimicrobials have been suggested to control pathogenic and spoilage bacteria on a variety of meat products. In this study, edible zein‐based coatings incorporated with nisin and lemongrass essential oil (LG) (8%) were evaluated for antibacterial action against L. monocytogenes and spoilage organisms on cold‐smoked, cultured hybrid striped bass, Morone saxatilis × Morone chrysops, under polyvinyl chlorine (PVC) and vacuum packaging for 14 days (PVC) and 42 days (vacuum packaging), respectively, at 4°C. In this study, corn zein‐based edible coatings were found to be an effective carrier for nisin and LG. Nisin‐treated samples were most effective against L. monocytogenes in both PVC and vacuum‐packaged fillets, with a total reduction of 3.5 log and 3.7 log, respectively over the length of the storage time. LG‐treated samples reduced L. monocytogenes cell counts by 2.5 log in PVC and 1.7 log in vacuum‐packaged samples. Only LG‐treated samples packaged in PVC were found to inhibit the growth of spoilage organisms. Because nisin‐ and LG‐treated fillets reduced L. monocytogenes, they may be useful methods to improve food safety in smoked seafood.     

Influence of Chitosan Nanocomposite and Rosemary (Rosmarinus officinalis L.) Extract Coating on Quality of Huso huso Fillet Inoculated with Listeria monocytogenes During Refrigerated Storage

This study aimed to evaluate the antilisterial and antioxidative effects of chitosan nanocomposites and rosemary extract coating on the fillet of Huso huso inoculated with Listeria monocytogenes during refrigerated storage (4°C). Fish fillets were subjected as control (without coating), 0.5% rosemary extract (RE), 1% chitosan (CS), and combination of chitosan and rosemary extract as chitosan nanocomposite (CS/RE). Then, samples were inoculated with L. monocytogenes. Subsequently, the chemical parameters (total volatile basic nitrogen (TVB-N), peroxide value (PV), pH, and thiobarbituric acid (TBA)) and antilisterial effects of coatings were monitored during 16 days of storage at 4°C. According to the results, CS/RE demonstrated a significant (p < 0.05) ability to inhibit the growth of L. monocytogenes from 4.14 log cfu/g to 2.23 log cfu/g at the end of the storage period, followed by CT and RET treatments, respectively, compared to the control. Even though samples coated with CS/RE had the lowest pH and TVB-N values (p < 0.05), this coating was not able to pause the protein denaturation after 8 days of storage (p > 0.05) compared to the other treatments. On the other hand, CS/RE coating retarded lipid oxidation by decreasing PV and TBA production in the samples compared to the control up to the end of refrigerated storage (p < 0.05).     

Biopreservative effect of pediocin ACCEL on refrigerated seafood

To investigate the biopreservative effectiveness of pediocin ACCEL on refrigerated seafoods, fresh fish fillets were immersed in various concentrations of pediocin ACCEL and then stored at either 4° or 0°C. Samples treated with nisin were used as a positive control. The aerobic plate counts (APC) of samples with bacteriocins were <2.0 log₁₀cfu/g (log cfu/g) after 2 days storage at 0°C, except that with 1500 IU/mL of pediocin ACCEL. The APC of samples with nisin were >2.0 log cfu/g after 2 days storage, while those with pediocin ACCEL occurred after 1 day storage at 4°C. In refrigerated seafoods, pediocin ACCEL and nisin suppressed the growth of inoculated Listeria monocytogenes during 2- and 1-week storage at 4°C, respectively. Compared with nisin, the pediocin ACCEL was considered to be more effective on the suppression of L. monocytogenes growth in refrigerated seafoods during 2-week storage at 4°C.     

Evaluation of the immune response in rainbow trout fry,Oncorhynchus mykiss (Walbaum), after waterborne exposure to Flavobacterium psychrophilum and/or hydrogen peroxide

The immune response in rainbow trout fry against Flavobacterium psychrophilum was elucidated using an immersion‐based challenge with or without prior exposure to hydrogen peroxide (H₂O₂). Samples were taken from the head kidney 4, 48, 125 and 192 h after immersion, and the regulation of several genes was examined. Bacterial load was assessed based on the presence of 16S rRNA and correlated with gene expression, and the levels of specific antibodies in the blood were measured 50 days post‐infection. Separately, both H₂O₂ and F. psychrophilum influenced gene expression, and pre‐treatment with H₂O₂ influenced the response to infection with F. psychrophilum. Pre‐treatment with H₂O₂ also affected correlation between gene regulation and pathogen load for several genes. A delay in antibody production in H₂O₂‐treated fish in the early phase of infection was indicated, but H₂O₂ exposure did not affect antibody levels 50 days post‐infection. An increasing amount of F. psychrophilum 16S rRNA was found in the head kidneys of infected fish pre‐treated with H₂O₂ relative to the F. psychrophilum group. The results show that a single pre‐treatment with H₂O₂ impairs the response against F. psychrophilum and may intensify infection.     

Microbial Quality,Safety, and Sensory Acceptability of X-ray Treated Fresh Channel Catfish Fillets

This study was designed to determine if treatment with low dose X‐ray irradiation changes microbial quality (microbial load), safety (Listeria monocytogenes incidence), and sensory characteristics (aroma, appearance, and texture) of fresh aquacultured Channel catfish (Ictalurus punctatus) fillets during refrigerated storage. Fillets were treated to 0, 0.5, 1.0, and 1.5 kGy using an X‐ray irradiator and stored at 3°C for 17 days. Fillet aerobic plate count (APC), psychrotrophic plate count (PPC), total coliform count (TCC), and L. monocytogenes incidence were measured every 4 days during storage. A Difference-From-Control test was used to measure aroma, appearance, and texture. Fillet microbial counts were significantly different (p < 0.05) with time, irradiation dose, and the interaction of these two treatments. As expected, APC, PPC, and TCC increased as storage time increased. Overall L. monocytogenes incidence was 40%, 27%, 0%, and 7% at 0, 0.5, 1.0, and 1.5 kGy, respectively. Aroma of irradiated and non‐irradiated catfish fillets was significantly different, with greater aroma differences recorded as storage time increased due to progressional spoilage of the untreated controls. However, there were no significant aroma differences noted among the different irradiation doses. Neither appearance nor texture was significantly different between any treatments throughout testing. This study indicated that exposure to low dose X-ray irradiation improved the microbial quality and safety of fresh catfish fillets without affecting sensory acceptability at time of purchase.     

Incidence of Pathogenic Microorganisms in Aquacultured Rainbow Trout (Oncorhynchus mykiss)

ABSTRACT

Quantitative levels of six known pathogens (Listeria monocytogenes, Clostridium botulinum, Salmonella species, Vibrio cholerae, Yersinia enterocolitica, and Y. pseudotuberculosis) and aerobic plate counts were measured at five aquaculture facilities. The farmed rainbow trout (Oncorhynchus mykiss) and trout fillets were sampled at two different growing seasons to monitor for microbial hazards. Listeria spp. was identified in both whole trout and trout fillets from all five facilities sampled from both growing seasons. Presumptive Clostridium botulinum spores were also identified from all five facilities for both seasons. The growing season did not affect pathogen levels and there was no evidence that any one aquacultural system was superior to the others. Salmonella spp., Vibrio cholerae, and Yersinia spp. were not isolated from any of the trout samples analyzed.     

Prevention of fungal infestation of rainbow trout (Oncorhynchus mykiss) eggs using UV irradiation of the hatching water

Fungal infestation by water mold Saprolegnia spp. causes great losses in aquaculture and fish egg hatching. To find a safe and effective alternative for the fungal prevention, we studied continuous disinfection of the inlet water by UV irradiation and ozonation combined with low concentration hydrogen peroxide (H₂O₂) treatments in a rainbow trout (Oncorhynchus mykiss) egg hatching system. High dose of UV irradiation (400 mWs/cm²) of the inlet water decreased the mortality of rainbow trout eggs from the 77.3% to 14.3% in a 28 day trial. UV irradiation did not modify water quality parameters, while combination of UV irradiation and H₂O₂ caused up to fivefold increase in the formate levels, and combination of O₃ and H₂O₂ caused even ten-fold increase in the acetate and formate levels. UV suppressed the gradual increase of the heterotrophic bacterial counts on the fish eggs. Based on the molecular profiling high dose of UV reduced the growth of some of the dominating bacterial groups and combination of UV and H₂O₂ had a distinctive effect on the overall bacterial community structure on the fish eggs.     

Different Packaging Conditions to Improve Shelf Life of Filleted Gilt-Head Sea Bream (Sparus aurata)

Abstract

Shelf life of cultured gilt-head sea bream fillets (Sparus aurata) in over-wrap, vacuum and gas mixture packages stored during 27 days at 1±1°C was compared. The gas mixtures used contained CO₂, O₂, and N₂ at different percentages (0% O₂ + 50% CO₂ + 50% N₂; 10% O₂ +50%CO₂ +40%N₂;20%O₂ +50%CO₂ +30%N₂;30%O₂ +50% CO₂ + 20% N₂).

The evolution of the freshness degree of the packaged fillets was carried out by measurements of total volatile bases (TVB), trimethylamine (TMA), Tiobarbituric Acid Reactives Substances (TBARS), K _i and H values, psychrotrophic bacterial counts and sensory evaluation (color, odor, flavor).

Fish fillets were obtained 3 hours after harvesting with the best handling practices. As a consequence of this, the initial bacterial load was very low. The inhibitory effect of CO₂ on bacterial growth was very effective, keeping very low counts throughout all the storage period. Gas packages without O₂ and vacuum packages presented very low oxidation, whereas TBARS values in over-wrap and 10%, 20% and 30% O₂packaged fillets increased according to the oxygen content in the package. K_i value and specially H value differentiated very well among aero-bically stored fillets, vacuum and modified atmosphere packaging. TVB and TMA productions were poor freshness indicators, since no differences were found among treatments. Sensory quality of fillets deteriorated faster in over-wrap than in vacuum and gas packages. Modified atmospheres containing 20 and 30% O₂ were given lower sensory scores than vacuum packages, since they gave rise to yellowness of the fillets and off-odors and off-flavors.

In summary, modified atmosphere packaging of filleted gilt-head sea breams with a gas mixture consisted of 50% CO₂ + 50% N₂ gave rise to an important extension of shelf life compared to over-wrap packaging, vacuum and modified atmosphere packaging with gas mixtures containing O₂. This was due to the very low oxidation levels produced during the storage, the lower H value as a consequence of a minor production of Hx and the great inhibition on microbial growth.     

氧化应激对鲤抗氧化状态和免疫功能的影响

为探讨氧化应激对鲤抗氧化状态和免疫功能的影响,本实验以H_2O_2作为活性氧自由基(ROS),将鲤暴露于不同浓度的H_2O_2(0、0.25、0.50和1.00 mmol/L)中,诱导鲤产生氧化应激反应。连续暴露7 d后,采集鲤血液和肝组织,以检测相关生化指标以及基因表达量的变化。结果显示,与空白对照组(0 mmol/L)相比,随着H_2O_2浓度的升高,血清葡萄糖(GLU)、皮质醇(cortisol)和乳酸(LA)含量显著升高;而碱性磷酸酶(AKP)和酸性磷酸酶(ACP)活性仅在1.00 mmol/L H_2O_2处理组中显著高于其他实验组。氧化应激参数显示,与空白对照组(0 mmol/L)相比,0.50和1.00 mmol/L H2O2处理显著降低血清过氧化氢酶(CAT)活性,而提高还原型谷胱甘肽(GSH)、丙二醛(MDA)和总抗氧化能力(T-AOC)水平;在肝脏组织中,1.00 mmol/L H_2O_2处理显著降低了GSH含量,促进了MDA生成。基因表达结果显示,与空白对照组相比,1.00 mmol/L H2O2处理组显著上调了肝脏组织中cyp1a表达,而下调了cyp1b表达;同时0.50和1.00 mmol/L H2O2处理显著上调了hsp70、hsp90、c3、c-lyz和hep的表达。研究表明,氧化应激暴露可诱导鲤产生明显应激反应和脂质过氧化,降低机体抗氧化能力并激发免疫应答反应。     

Comparative Evaluation of Natural Antioxidant Coating and Vacuum-Packaging Technique on Quality Characteristics of Chill Stored Giant Trevally Fillets

ABSTRACT

The effect of coating with natural antioxidants like sage and oregano essential oils (EO), and tocopherol on spoilage characteristics of giant trevally fillets was evaluated during chilled storage. Further, results were compared against vacuum and conventional polyethylene packaging practices. Prior to coating, the properties of antioxidants were evaluated in vitro using standard activity assays. Coating with EO was found effective in retarding lipid oxidation in fish fillets; while tocopherol accelerated the spoilage process. It was concluded that EO treatment can slow down the process of spoilage in fish fillets and can be considered as an alternative to expensive vacuum-packaging technique.     

The Effects of Chitosan Coating on Biogenic Amines Inhibition and Microbial Succession of Refrigerated Grass Carp (Ctenopharyngodon idellus) Fillets

Chitosan coating and plastic wrap coating were investigated for their effects on the quality of grass carp fillets stored at 4 ± 1ºC for a period of 20 days. The fillets were divided into groups of untreated (Control), wrapped with sterile preservative film (PE), and chitosan-treated (1, 2, and 2.5% w/v corresponding to CH1, CH2, and CH2.5, respectively). The final result demonstrated that chitosan coating has positive effects on the microbial inhibition of total volatile count (TVC), lactic acid bacteria (LAB), Enterobacteriaceae, Pseudomonas, H₂S-producing bacteria (including Shewanella putrefaciens), and Staphylococcus. With regard to the results of biogenic amines (BAs), putrescine (PUT) and histamine (HIS) were the major amines, and their concentration was significantly (p < 0.05) higher in Control and PE than in chitosan-coated fillets at the end of storage. The final concentration in Control, PE, CH1, CH2, and CH2.5 was 143.7, 160.1, 83.0, 59.4, and 44.2 mg/kg for PUT and 228.0, 57.1, 4.1 3.2, and 2.9 for HIS, respectively. Chitosan coating was found to inhibit the increase of total volatile base nitrogen (TVB-N), microbial population, and total BAs and prolong the shelf life of grass carp fillets. However, sterile plastic wrap coating had little positive effect on maintaining the quality of grass carp fillets during refrigerated storage.     

Response of Rainbow trout (Oncorhynchus mykiss) to unrefined peanut oil diets: Effect on growth performance,fish health and fillet fatty acid composition

A 60‐day feeding study with rainbow trout, Oncorhynchus mykiss, was conducted to determine the effects of replacement of fish oil (FO) by unrefined peanut oil (PO) on growth performance, feed utilization, body composition, fatty acid composition and serum biochemical and haematological parameters. Rainbow trouts (51.60 ± 0.75 g) were fed five experimental diets formulated by replacing dietary FO with PO at levels of level 0 (PO₀), 1/4 (PO₂₅), 1/2 (PO₅₀), 3/4 (PO₇₅) and 4/4 (PO₁₀₀), respectively. As a result, the best growth performance was observed in fish fed with PO₀ and PO₅₀ diet. No significant differences were detected among the groups in terms of body compositions. Fatty acid profiles of the fish fillets reflected the fatty acid profiles of the feeds that the fishes were fed with. In this study, the haematological parameters detected that there were no significant differences compared to the control group, whereas the serum biochemical parameters generally worsened as the ratio of peanut oil in the ration exceeded half of fish oil. As a conclusion, the results of the study suggested that the unrefined peanut oil could be used as a replacer of fish oil in diets for rainbow trout.